It would make sense - but I suspect that you can have your transistors custom-coloured to all sorts of specs, depending on what you need. I believe that this is an additional service from certain manufacturers...

It could also be some kind of selction done by the gear manufacturer. I recently talked to a Neumann deveolper. He told me that they put color dots on rejected tubes when they select them for noise. At some point they noticed they received again many of the tubes they already rejected on earlier orders.

I'll have a look at what the colours actually are. BTW, it's about the MPSA14, darlington. Couldn't imagine it matters much for most circuits whether the gain is above 10,000 or above 20,000...

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I recently talked to a Neumann deveolper. He told me that they put color dots on rejected tubes when they select them for noise. At some point they noticed they received again many of the tubes they already rejected on earlier orders.

Uh, so the bad ones got out anyway and showed up again in problematic units ?

Those striped codes were popular with Motorola and maybe others but I never knew what they meant ;-)

However, they are implied in many Japanese parts such as Toshiba in their beta or Idss sorts: Y, GR, BL, V for yellow green blue violet. But I have never seen a Toshiba transistor with an actual color band on it.

In small volume manufacturing we used to paint red on the tops of PNPs because of the constant screwups if we didn't (hand-insert errors). Then I introduced JFETs and caused a hue and cry---they had to start using blue paint and even some other colors.

Those striped codes were popular with Motorola and maybe others but I never knew what they meant ;-)

However, they are implied in many Japanese parts such as Toshiba in their beta or Idss sorts: Y, GR, BL, V for yellow green blue violet. But I have never seen a Toshiba transistor with an actual color band on it.

Me neither. Luckiliy the Y,GR etc are added to the marking, so all is good.

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In small volume manufacturing we used to paint red on the tops of PNPs because of the constant screwups if we didn't (hand-insert errors). Then I introduced JFETs and caused a hue and cry---they had to start using blue paint and even some other colors.

I recall seeing Japanese PNP's sometimes having green plastic - good move. I thought I've seen green regulators (neg) as well. And pink elephants, no, green double diodes as opposed to double ones in black for the 'normal' connection.

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and even some other colors

Let's hope it was transparent paint :wink: - well, I mean, at least Philips discretes have had their marking on top in the past for a while.

Uh, so the bad ones got out anyway and showed up again in problematic units ?

They didn't use the ones that didn't pass the test. The rejected ones were returned or resold. Which I think is nicer than simply destroying them. A tube rejected by Neumann for, say, a U67 reissue isn't necessarily unusable for anyone else. The only problem was that the same tubes that some of the tubes they rejected turned up again in another shipment. So they put color dots on each tube they tested. When they receive a new shipment they can at least save some time by sorting out the ones they already tested.

They didn't use the ones that didn't pass the test. The rejected ones were returned or resold. Which I think is nicer than simply destroying them. A tube rejected by Neumann for, say, a U67 reissue isn't necessarily unusable for anyone else. The only problem was that the same tubes that some of the tubes they rejected turned up again in another shipment. So they put color dots on each tube they tested.

Thanks Rossi. Ah I see, so those manufacturers just kept trying...Indeed a pity to destroy them.

from CJ:

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What are you going to use the MPSA14 for?

It's the suggested darlington for the JFP. Generic darlington is stated to be OK, but since I have a few of these MPSA14 anyway then why not use that one. (Motorola, but all kinds of different colours... :cry:/ :grin: )